Wow, lots of great ideas here, I love the idea of looking at it like medication. It especially appeals to me because I'm on the fence about going back on meds after 6 years managing passably without them. I'd prefer to keep things holistic if I can, though I know it may not be an option forever. So telling myself "It's this or prozac!" could be the push I need! (No offense intended to anyone who needs meds, I'm in no way against them morally or anything like that, it's just a personal preference after spending my teen years on various meds.)
There are a couple ways I help push myself to exercise when I'm too down. First, I
make it fun. I bought a Gazelle Edge - a reasonably cheap, reasonably small piece of exercise equipment. It's basically an elliptical, though I think technically it's not a "true" elliptical. Anyhow, it's more fun than a treadmill, to me. Not loads of fun, but slightly reminiscent of swinging on a swingset as a kid. Because I exercise at home, I don't have to worry what people think of how I look, so I just throw on some sweats or whatever looks comfy. Also, I always watch the most indulgent, silly, nostalgic TV shows I can think of audio-visual junk food/comfort food, which for me is usually the cartoons I watched when I was little - or cartoons I would have watched as a kid if they'd been on. I love The Fairly Oddparents!
I also like to
make bargains with myself. When my inner voice of depression says "I don't wanna" I tell it "You'll feel better if you at least try. How about just doing half the usual time?" Sometimes "we" have to barter quite a bit, and my depressive voice will only agree to do five minutes. But fairly often, like 4 outta 5 times, I end up thinking "Oh ok, this isn't so bad" (especially with the "make it fun" stuff above) and end up doing the whole thing. And when I don't, it's ok, because I beat myself up a lot less the next day knowing I at least tried.